Marinate. Soak the chicken pieces in the buttermilk in a very large bowl. Refrigerate for at least 6 hours, up to 12 hours.
Bread. Combine the flour, salt, pepper, and seasoned salt in a large mixing bowl. Take out the chicken pieces, shaking off the excess buttermilk, and dredge them in the seasoned flour, one by one.
Chill. Place the floured chicken pieces on a wire cooling rack set over a rimmed baking sheet. Refrigerate, uncovered, for at least 2 hours to help the flour stick.
Fry. Preheat the deep fryer to 340 degrees (or use a heavy-duty Dutch oven filled with three inches of oil and use a candy thermometer to monitor the temperature). Fry the chicken, covered, for 12-15 minutes per side until golden brown and thoroughly cooked. The internal temperature should be at least 165.
Serve. Place a clean cooling rack over a baking sheet with layers of paper towels. Place the cooked chicken on top and allow to drain. Serve immediately, or hold in a 200-degree oven.